Hypoxic-ischemic (H-I) injury to the neonatal brain is a major cause of morbidity and mortality. Recent work from animal models suggests that while a large amount of neuronal cell death is due to excitotoxicity and occurs rapidly, a major portion of the cell death also occurs in a delayed fashion, has features of apoptosis, and is caspase-dependent. Our data suggests that the executioner caspase, caspase-3, may be a critical caspase required for the apoptotic-like neuronal cell death following neonatal H-I. Our data also suggest that the amount of caspase-3 like activation in the developing brain is much more marked than in the adult brain following similar H-I insults. Utilizing a well characterized neonatal model of H-I in both rats and mice, we estimate that about 50% appears to be caspase-independent. Given the degree and the delay in much of the cell death following neonatal H-I and the fact that neonatal H-I insults are often transient, injury to the neonatal brain appears to be an ideal paradigm to both better understand and to develop model treatments based upon a combination of both caspase and non-caspase dependent treatments. Our recent data suggests that a secreted protein known as clusterin appears to contribute in an important way to non-caspase dependent cell death following neonatal H-I. The mechanism by which clusterin contributes to death is not yet clear. A better understanding of the molecules which contribute to caspase-dependent and independent injury is likely to lead to a better understanding of pathogenesis as well as development of novel therapies. We hypothesize that caspase-3 activation is required for the majority of caspase dependent neuronal death observed following neonatal H-I and that clusterin and p38 MAP kinase signaling contribute to the non-caspase dependent death. In order to test the involvement of specific molecules in the cell death pathway in vivo as well as intracellular signaling events and mechanisms underlying cell injury, we will utilize both rat and mouse models of neonatal H-I with which we have worked extensively and well as pharmacological inhibitors in the following aims: Aim 1: To determine and optimize the ability of novel, potent caspase-3 inhibitors in neonatal H-I to block injury. Aim 2. To determine the endogenous intracellular signaling pathways which contribute to brain injury following neonatal H-I, particularly the p38 pathway utilizing pharmacological inhibitors. Aim 3: To determine the mechanism by which clusterin contributes to non-caspase-dependent neuronal cell death. Aim 4: To characterize baseline behavior and anatomy of clusterin -/- and caspase 3 -/- mice at baseline and to determine the role of clusterin and caspase-3 in neonatal H-I injury.